1. Field of the Invention
The invention relates to an information transmission system for the simultaneous transmission of analog or digital baseband signals, for example, POTS, ISDN, etc., and of broadband signals, for example ADSL, VDSL, etc., via a two-wire line from a central office, for example an automatic exchange, to at least one subscriber, with a baseband unit and a broadband unit that are connected by at least one hybrid circuit and at least one broadband filter formed of a high-pass and a low-pass filter with the subscriber line.
2. Description of Related Art
At the present time, known systems of this type exist, for example, in automatic exchanges of the public telephone network, whose operators offer broadband transmission capability for certain subscribers, as needed. But broadband service can be provided to subscribers not only in automatic exchanges but also in remote automatic exchanges connected to the former via a transmission link.
Broadband technologies, such as ADSL, VDSL, and xDSL, etc. use the frequency band above the baseband, which is used, for example, by POTS (Plain Old Telephone) or ISDN signals. These various transmission services use the same subscriber line as the transmission medium.
To give an example, the ADSL (asymmetric digital subscriber line) broadband transmission technology, which is becoming more and more popular, enables digital information transmission of large volumes of data via a two-wire subscriber line in one direction from the central office to the subscriber and the transmission of control functions in both directions. Currently, ADSL information transmission systems frequently use QAM technologies, for example DMT (discrete multiple tone modulation) or CAP (Carrierless phase modulation), whereby the formed signals overlie the analog or digital telephone signals, for example, POTS or ISDN, with respect to frequencies. The signal transmitted or to be transmitted is split via special broadband filters (ADSL filters) for receiving and superposed for transmission, both on the exchange side and the subscriber side.
At the central office, for example, the automatic exchange, the baseband unit, the broadband unit, and their common broadband filter are arranged separate from each other in different spatial areas; the different transmission units in the past were considered to be completely separate function blocks, which therefore also sometimes were arranged at points far apart within the automatic exchange.
The disadvantage of known information transmission systems of this type is therefore that the spatial separation results in significant wiring expenditures and requires additional space because of separate filter assemblies and separate racks for broadband or baseband units. Wiring expenditures hereby include not only the actual cross-connection work within the automatic exchange but also the documentation of how the individual, installed lines are associated with the interconnected units. These records constantly must be adjusted to the changes that are gradually made over time and require the archiving of data and maintenance of the archived data.
This means that the additional cost of maintenance resulting from each wiring, which manifests itself especially in personnel costs, is very important. The costs for the individual cross-connection points within the automatic exchange are also significant.
Another disadvantage is due to the fact that a separate processor control must be provided both for the broadband unit and for the baseband unit.
The objective of the invention is to describe an information transmission system of the initially mentioned type, which enables a reduction in the required space and wiring expense at the central office, especially with respect to cross-connecting and maintenance work.
Another objective is to reduce the preventive maintenance expense and equipment costs, for example, for cross-connection points, of the system, and of the number of individual interface controls for the system.
Another objective of the invention consists of creating an information transmission system in which existing transmission units can be easily adapted to additional, new ones.